


Nightmare's Tentacles

by carelesscreativity



Category: Undertale (Video Game)
Genre: Blow Jobs, Crosstale Sans (Undertale), Dreamtale Nightmare Sans (Undertale), Dubious Consentacles, Forced Masturbation, Killer Sans (Undertale) - Freeform, M/M, Other
Language: English
Status: Completed
Published: 2020-10-30
Updated: 2020-10-30
Packaged: 2021-03-09 03:35:29
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 1,943
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27278095
Author URL: https://archiveofourown.org/users/carelesscreativity/pseuds/carelesscreativity
Summary: Nightmare's tentacles being self-aware.
Relationships: Krossmare - Relationship, Sans/Sans (Undertale)
Comments: 3
Kudos: 104





	1. Part One

**Summary for the Chapter:**

> Nightmare's tentacles have fun with him.

The dark skeleton’s hand paused. He had to stop writing as one of his tentacles flicked. Nightmare had not flicked it himself. Sometimes this happened. He lost control of his own corruption and it did whatever it pleased. He placed the pen down on the desk. He knew better than to write when his tentacles were like this. He’d learned from last time.

He inhaled quietly. He closed his eye and tried to pull them back under his control. He had work to do and this would slow him down greatly. He furrowed his brow, only to shiver as one of his tentacles slipped into the top of his sweater, wiggling down against his neck. Another slipped between his legs, sliding easily into the waistband of his shorts.

He jerked a little in his chair. His bony fingers dug into the armrests and he forced himself to remain quiet. If he seemed uninterested, the tentacles would stop. He’d managed to stop them like that once before. Unfortunately, they seemed to have learned. The one in his shorts wrapped around the front of his pelvis, rubbing it. His legs shook.

The last two tentacles made their way down and curled around his femurs, both forcing his legs to open all the way. The tentacle in his shirt appeared out the bottom, beginning to pull it up. Nightmare inhaled sharply. He reached up and grabbed his tentacle, forcing it to stop. “I have work to do!” He hissed. The tentacle flicked in his hand.

The one around his pelvis gave a tough grind and Nightmare gasped, his face heating up. They all seemed to wiggle and Nightmare swore internally, knowing they were excited now. He drew in another shaking inhale. The tentacle in his hand lunged forward, forcing itself past his jaws and making its way into his throat. Nightmare choked and the shock overwhelmed him.

He lost control and his ecto began to form, the tentacles all becoming heavily excited. Nightmare was trying to breathe around his own appendage, his eye wide. He was beginning to tear up. He was still overwhelmed and his ecto reacted as such. It formed everything. From his breasts to his cock. He made a noise of protest as his tentacles pulled his shorts down to his ankles. They still wouldn’t let him get up.

His tentacles didn’t seem to mind the ecto, immediately beginning to explore the new areas. Nightmare reached up and tried to pull the tentacle out of his mouth, only for two more tentacles to form from his back and slam his wrists back down against the armrests. He jerked. One tentacle slipped between his breasts, coiling around both of them. It gave them a squeeze and it was rewarded with a muffled groan.

Another had coiled around Nightmare’s cock while the last had slipped up against his folds, rubbing in between them. Nightmare’s thighs twitched as two more newly formed appendages forced them open again. Nightmare arched his back. His head was forced back as the tentacle in his mouth slowly began to thrust. The one at his entrance was rubbing in time with the thrusts.

Nightmare let out a weak moan, his body shaking. His breasts were squeezed again and he trembled, gasping. The tentacle pushed inside of his entrance without warning and he jerked, his thighs still forced wide open. He let out a loud, muffled moan, tears welling in his eyesocket. The tentacle under him began to thrust and Nightmare cried out again.

He was desperately trying to remember if he’d locked the door. He knew his crew would knock… MOST of his crew would knock. He screwed his eyes shut. He’d only ever told Dream his tentacles did this. He’d scoffed at the idea that he might be pent up and frustrated, but it didn’t seem as ridiculous now. He let out a soft shriek as the tentacle inside him pushed deeper, practically inside his womb.

His eye was wide. The tentacle pulled itself out of his mouth and he kept his jaws open for air. It was a mistake. The tentacle inside him began to thrust mercilessly, making him shriek and the sound deteriorated into a loud moan. He leaned forward, shaking as his breasts were squeezed, along with his cock. A flash caught his eye.

He couldn’t look away now. He stared at himself tearfully in the mirror. “Fuck…” He whimpered. He couldn’t see what was happening beneath, but he could see himself being wrecked by his own appendages. The first tear escaped down his face and he grit his teeth. Something thin slipped over the tip of his cock and he froze up.

He didn’t have time to react before the tendril was inside, pushing its way into his cock. Nightmare screamed, finally hunched against the desk. He moaned as the tendril in his cock and the tentacle in his entrance began to thrust and he wailed. His fingers dug into the armrests, his wrists still pinned. He was shaking and overstimulated.

“Pl-Please! F-Fuck!! Ah!!” He was loud and too overwhelmed to care as he broke loose. The tentacles seemed to like that. He wanted to cum. He was already crying. He opened his jaws but couldn’t get the words out. He tried to buck his hips in an effort to dislodge the tendril, but it did no good. “P-Please…! C-Cum!! L-Let me c-cum!!” He begged tearfully.

There was a moment of nothing before the tendril thrusted DEEP before suddenly yanking itself out and Nightmare screamed as he came, his cum coating his chair and the underside of his desk. He shook violently, slumped over the desk. He realized something. None of the tentacles were loosening. It seemed he was in for a long night.


	2. Part Two

**Summary for the Chapter:**

> Killer and Cross join in.

“Killer! It’s not our fucking business!!” Cross insisted as he moved after the other, his cheeks slightly flushed. “We can’t just fucking barge in on him!!” Killer snorted and turned to him, almost making Cross crash into him.

“C’mon! Aren’t ya even a LITTLE curious about Boss havin’ a partner at this hour?? Don’t you wanna see who it is?? Or are you just upset it ain’t you?” Cross was momentarily taken back and Killer grinned. “I’m not stupid, Cross. You OBVIOUSLY fell for ‘em!” Cross stared at him before muttering that he hadn’t. “BULL. SHIT.”

He growled as Killer spoke. Killer stared at him for another moment. They both perked up as another muffled moan drifted through the hall from the study door. “Besides, I’M curious to who’s topping.” Killer began to move swiftly forward again.

Cross jumped and tried to pull him back. Killer reached the door and knocked briskly. Cross thought he heard choking for a moment. Killer opened the door without anyone saying he could and Cross began to scold him before stopping cold. Nightmare was shaking, bent over the desk. His chair had fallen over behind him, forcing him into a standing position. His ecto was fully formed and his tentacles had restrained his wrists behind him.

Cross couldn’t help but stare for a moment, a flare felt in his chest and pelvis. He immediately turned away, averting his eyes. Nightmare was panting shakily, gasping as the tentacle inside his dripping cunt curled a little. Killer whistled softly as he stared at him. “Damn, Boss…” He shut the door. “I always suspected you could use them like this, but I never thought I’d get to see it.”

There was an angered hiss and Killer chuckled. Cross spoke in a strangled voice, saying that they should go. Nightmare let out a sharp, shaking moan and Cross visibly shook. “Really? Yer just gonna leave him like this?” Killer sounded incredulous. He began to move forward and Cross grabbed him.

“Don’t!” He growled. Killer scoffed, beginning to pull away. Cross shoved him backwards, summoning his knife and pointing it at him. He glared at Killer, who seemed actually taken back before a grin curled the side of his mouth. A tentacle had slipped itself around Cross’ waist and he yelped as he was yanked backwards.

The tentacle lifted him over the desk, settling Cross next to Nightmare. The soldier immediately knelt next to Nightmare, trying to figure out if he was okay. “B-Boss?” He asked shakily. Nightmare inhaled sharply.

“Out… get it out…” He spoke in a strained, raspy voice and Cross nodded. He gulped and asked if he could touch him. Nightmare gave a spastic nod. “Hurry!!” Cross jumped and got up. He gulped and reached between Nightmare’s legs from behind. He placed his other hand on Nightmare’s ass without thinking, wanting to hold him still.

Nightmare made a weak noise and Cross flushed to his shoulders, apologizing. He gripped the tentacle that was in Nightmare’s entrance and began to pull it out. It made slick, wet noises and Nightmare moaned, making Cross shudder a little. The flare in his pelvis spread and he felt ashamed as his cock began to form. He pulled the tentacle all the way out and Nightmare’s thighs visibly twitched.

His entrance was DRENCHED and Cross’ cock throbbed at the sight of it. He gave a dry gulp. Another tentacle had guided Killer over. The tentacles suddenly dragged Nightmare slightly backwards, making him jump in shock. His cock exposed itself, looking painfully hard. Killer blinked as a tentacle settled on his shoulders and began to force him down.

Nightmare panted, his body shaking. Killer tipped his head and moved underneath Nightmare. He seemed to understand what the tentacle wanted him to do. “Oh, this is gonna be fun…” He purred. He was grinning. Cross could tell that much from his tone. “I’ll do my best, Boss.”

His breathing became muffled as Nightmare jerked, gasping, his eye widening. Killer’s noises were muffled, having taken Nightmare’s cock all the way into his throat. He was holding Nightmare’s hips. Another tentacle flicked against Cross’ cheek, making him snap back to attention. He had his fingers curled into the sides of his shorts.

The tentacle wrapped around Cross’ waist and practically dragged him over behind Nightmare. Right there. The tentacles around Nightmare’s thighs pulled them apart, spreading the entrance for Cross. Cross shook a little and exhaled. “B-Boss? You really want me to…?” The tentacle seemed to impatiently yank him closer and Cross nodded. He pulled his shorts down, exposing his cock.

He gulped. He reached out and held Nightmare’s hips, rubbing circles. That seemed to calm Nightmare’s shaking a little. He jerked beneath Cross’ touch, but based on the muffled chuckle from Killer, it hadn’t been from anything Cross did. Nightmare moaned and cried out, his body twitching. The tentacle around Cross’ waist pulled him closer, seeming very impatient.

His cock brushed Nightmare’s folds and he could feel how wet he was. “I-I’ll do my best.” He mumbled, echoing Killer as he pushed his cock into his trembling boss. Nightmare’s eye widened and he cried out in shock. Cross grunted, inhaling shakily as Nightmare squeezed around him. Nightmare’s body shook and Killer was heard momentarily choking.

“Cross…” Cross froze up as Nightmare groaned his name. He yelped as Nightmare tightened on him again. “Come on! Fucking MOVE!!” He sounded frustrated and moaned. Cross’ throat went dry and he nodded.

“Y-Yes, Boss.” He began to move slowly at first. Nightmare groaned and his tentacles finally released his wrists. Nightmare’s hands immediately moved around to scrabble at the desk, gripping it tightly. Cross picked up the pace and it only made him more heated to feel their ecto slapping together. Nightmare was practically crying out both their names.

His tentacles gave the smallest hint of a wag behind him.


End file.
